Hyperthermia, either alone or in conjunction with radiation and/or chemotherapy holds considerable promise in cancer therapy. Critical evaluation or full clinical exploitation of this potential has hitherto not been possible due to lack of proven, reliable and safe techniques for production of tumor hyperthermia. A technique is now available for production of a controllable level of hyperthermia, restricted to the tumor vlume along and has been evaluated in normal tissues of the dog in vivo. A study of the effects of measured levels and durations of local hyperthermia on normal tissues and tumors transplanted in mice or occurring spontaneously in dogs is proposed. Temperature distributions in tumor, tumor bed and surrounding tissues will be measured. Effects on tumor growth and metastasization; morphological alterations and their sequelae, alterations in local blood-perfusion, oxygen concentration and pH will be studied in different regions of tumors and compared with those in normal tissues. Use of a Mass Spectrometer to simultaneously measure local O2, CO2 concentration and permeabilty changes will be evaluated. The feasibility of non-invasive debulking of large tumors, and thermal focusing of chemotherapeutic action to the tumor will also be studied.